Fine cellulose fiber dispersion liquid and manufacturing method thereof, cellulose film and laminate body

ABSTRACT

A method of manufacturing a fine cellulose fiber dispersion liquid includes: an oxidation process in which a cellulose is subjected to an oxidation treatment to obtain an oxidized cellulose; and a dispersion process in which the oxidized cellulose obtained in the oxidation process is subjected to a dispersion treatment in a water-based medium in which a pH thereof is adjusted to 4 to 12 using either an ammonia water or an organic alkali to obtain the fine cellulose fiber dispersion liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/583,126 filed Sep. 6, 2012, which is a U.S. national stageapplication of PCT/JP2011/054988 filed Mar. 3, 2011 and claims theforeign priority benefit of Japanese Application No. 2010-051616 filedMar. 9, 2010, Japanese Application No. 2010-157571 filed Jul. 12, 2010,Japanese Application No. 2010-157572 filed Jul. 12, 2010, and JapaneseApplication No. 2010-215966 filed Sep. 27, 2010 in the JapaneseIntellectual Property Office, the contents of all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a technique referring to a cellulosefine fiber available as a functional film base material, a coatingagent, or various additive agents, and relates to a dispersion liquidcontaining the cellulose fine fiber, a manufacturing method thereof, anda cellulose film and a laminate body obtained using the dispersionliquid containing the cellulose fine fiber.

BACKGROUND ART

In recent years, various natural polysaccharides, such as naturallyoccurring starch, cellulose, chitin/chitosan, and derivatives thereof,have attracted attention as biomass materials, relative to conventionalpetroleum-based resins, with increasing concerns about environmentalissues. In addition, base materials formed by biodegradable resins,which are decomposable into water and carbon dioxide in the environment,also attract attention and are commercially available. Specific examplesthereof include aliphatic polyesters yielded by microorganisms, variouspolysaccharides such as naturally-occurring starch, cellulose,chitin/chitosan, and derivatives thereof, biodegradable resinscompletely obtained by chemical synthesis, and polylactic acids obtainedby polymerizing lactic acid derived from a starch or other rawmaterials.

Among the above, the cellulose, which is yielded in the largest quantityon earth, attracts attention as a functional material, because thecellulose is fibriform, has a high crystallinity, a high strength, and alow linear expansion coefficient, and is excellent in chemical stabilityand living body safety. Particularly, a fine cellulose fiber has beenapplied in a paper-strengthening agent, a filter aid, a food additive,or the like, and actively developed in recent years.

As a manufacturing method of the fine cellulose fiber, Patent Document1, for example, discloses a fibrillating (pulverizing) method in which acellulose suspension is sprayed under a high-pressure of 100 MPa orhigher and thereby reducing the pressure.

Patent Document 2 discloses a method for obtaining a fine cellulosefiber by dispersing a cellulose in a medium, the cellulose havingcarboxyl groups obtained by partially oxidizing hydroxyl groups of thecellulose using a TEMPO (2,2,6,6-tetramethylpiperidinoxy radical)catalyst. The method makes it possible to obtain, with relative ease,the fine cellulose fiber having a type I cellulose crystalline structureby utilizing electronic repulsion of the carboxy groups having negativeelectrical charges.

Patent Document 3 disclose a method for obtaining an epoxy resincomposite by adding a modified fine cellulose fiber to an epoxy resin,the modified fine cellulose fiber being obtained by treating a finecellulose fiber with an organic onium compound, the fine cellulose fiberbeing obtained by dispersing a cellulose in a medium, the cellulosehaving carboxyl groups obtained by partially oxidizing hydroxyl groupsof the cellulose using a TEMPO catalyst.

Patent Document 4 discloses a method for obtaining a gas barriercomposite compact by coating and drying a gas barrier material on a PETfilm or a base material made of polylactic acid or the like, the gasbarrier material containing a fine cellulose fiber having an averagefiber diameter of 200 nm or less being prepared by dispersing in wateran oxidized cellulose obtained by a TEMPO oxidation treatment.

CITATION LIST Patent Documents

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2009-155772

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2008-1728

[Patent Document 3] Japanese Unexamined Patent Application, FirstPublication No. 2010-59304

[Patent Document 4] Japanese Unexamined Patent Application, FirstPublication No. 2009-57552

SUMMARY OF INVENTION Technical Problem

Although Patent Document 1 discloses that a fine cellulose fiber havingan average fiber diameter of 4 to 200 nm is obtainable, the fibrillationrequires several treatments under an extremely high pressure, and limitsavailable devices. In addition, it is difficult to efficiently obtain ahomogeneous fine cellulose fiber by performing only a mechanicaltreatment. In addition, although the fine cellulose fiber is disclosedto be used by being combined with a synthetic polymer, the use of thefine cellulose fiber alone is not disclosed.

The carboxyl groups in the method disclosed in Patent Document 2 areassociated with metal-ions, such as sodium ions, as counter ionsthereof, as disclosed in examples thereof. In the case where the finecellulose fiber is applied in an electronic component such as asemiconductor or a fuel cell, the presence of the metal-ions adverselyaffect on electronic properties thereof, and therefore is notpreferable. In addition, although the fine cellulose fiber is disclosedto be cast to form a self-supporting film, there are problems in whichthe fine cellulose fiber film containing the metal-ions as the counterions has a weak water resistance, and thereby being easily swollen withwater, which decreases in strength thereof.

Patent Document 3 discloses that the method makes it possible to obtaina fine cellulose fiber easily dispersible in resin by performing theorganic onium treatment in which metal-ions present as counter ions ofthe carboxyl groups are exchanged for organic onium ions. However, thefine cellulose fiber forms an aggregate during the ion-exchange process,which undermines the efficacy obtained by dispersing and pulverizing thecellulose at the process before the organic onium treatment. Even if thefine cellulose fiber once agglomerated is added in resin, the dispersionbecomes insufficient and the fiber diameter becomes non-uniform, whichmakes it impossible to obtain a homogeneous composite material havingboth a high degree of strength and a high degree of transparency.

In addition, a film formed using a water-based dispersion liquid of afine cellulose fiber, as disclosed in Patent Document 4, causes aproblem in which the adhesiveness of the film to a base material such asa PET film is low due to an extremely hard form and low reactivity ofthe fine cellulose fiber. For example, there is a case in whichinterlayer separation between a base material and an undercoat occurs,when the base material is a film base material, particularly formed by anaturally occurring material, such as polylactic acid, and the undercoatof the base material is formed using a conventional water-baseddispersion liquid of a fine cellulose fiber.

The above is caused because paper, polylactic acid, or other material isa natural product, which results in a chemical instability, bleeding oflow-molecular-weight molecules, crystallization, or surfacedeterioration, in comparison with petroleum-derived synthetic resins,such as PET, and thereby lowering the wettability and the adhesivenesswhen coated as the base material. Accordingly, it is difficult toimprove the adhesiveness between the film (undercoat) formed using thewater-based dispersion liquid of a fine cellulose fiber and the basematerial formed by a naturally occurring material such as polylacticacid.

The present invention has been made in view of the above-mentionedproblems, and it is an object thereof to provide a dispersion liquidcontaining a fine cellulose fiber, uniformly dispersible in an organicsolvent or a resin, and applicable in electronic components.

In addition, it is an object thereof to provide a cellulose film and alaminate body, obtained using a fine cellulose fiber having an improvedwater resistance.

In addition, it is an object thereof to provide: a fine cellulose fiberdispersion liquid for forming a film as an undercoat of a film basematerial, particularly a base material formed from a naturally occurringmaterial, such as polylactic acid, the adhesiveness of the film to thebase material being improved; and a laminate body formed using the same.

Solution to Problem

In order to solve the above-mentioned problems, a first aspect of theinvention defined is a fine cellulose fiber dispersion liquidcharacterized by containing at least: a fine cellulose fiber and eitheran ammonia or an organic alkali.

A second aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized in that the organicalkali is either an amine or an organic onium compound having ahydroxide ion as a counter ion.

A third aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized in that the organicalkali is a quaternary ammonium compound having a hydroxide ion as acounter ion.

A fourth aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized in that the finecellulose fiber is obtained by subjecting a cellulose to a dispersiontreatment in a water-based medium while adjusting the pH to 4 to 12using an ammonia water or the organic alkali.

A fifth aspect of the invention is the fine cellulose fiber dispersionliquid according to the fourth aspect, characterized in that thewater-based medium is either water or a mixed liquid containing thewater and an alcohol, and the alcohol is methanol, ethanol, 1-propanol,2-propanol, 1-butanol, or 2-butanol.

A sixth aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized by furthercontaining a water-soluble organic solvent.

A seventh aspect of the invention is the fine cellulose fiber dispersionliquid according to the sixth aspect, characterized in that thewater-soluble organic solvent is at least one organic solvent selectedfrom the group consisting of methanol, ethanol, 2-propanol, acetone,methyl ethyl ketone, 1,4-dioxane, tetrahydrofuran,N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide,acetonitrile, and ethyl acetate.

An eighth aspect of the invention is the fine cellulose fiber dispersionliquid according to the seventh aspect, characterized in that an amountof the water-soluble organic solvent is at least 0.1% by weight,relative to a total amount of the fine cellulose fiber dispersionliquid.

A ninth aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized by furthercomprising an additive agent containing a compound having a reactivefunctional group.

A tenth aspect of the invention is the fine cellulose fiber dispersionliquid according to the first aspect, characterized in that the finecellulose fiber is an oxidized cellulose having a carboxyl groupintroduced by oxidation reaction, and a content of the carboxyl group is0.1 mmol/g to 2 mmol/g.

An eleventh aspect of the invention is the fine cellulose fiberdispersion liquid according to the tenth aspect, characterized in that anumber-average fiber diameter of the fine cellulose fiber is 0.003 μm to0.050 μm.

A twelfth aspect is a cellulose film characterized by being formed bydrying the fine cellulose fiber dispersion liquid of any one of thefirst through eleventh aspects.

A thirteenth aspect of the invention is a laminate body characterized inthat a coating film is formed by coating the fine cellulose fiberdispersion liquid of any one of the first through eleventh aspects on atleast one surface of a base material.

A fourteenth aspect of the invention is the laminate body according tothe thirteenth aspect, characterized in that the coating film is anundercoat layer.

A fifteenth aspect of the invention is a manufacturing method of thefine cellulose fiber dispersion liquid, characterized by including: anoxidation process in which a cellulose is subjected to an oxidationtreatment to obtain an oxidized cellulose; and a dispersion process inwhich the oxidized cellulose obtained in the oxidation process issubjected to a dispersion treatment in a water-based medium in which thepH thereof is adjusted to 4 to 12 using either an ammonia water or anorganic alkali to obtain the fine cellulose fiber dispersion liquid.

A sixteenth aspect of the invention is the manufacturing method of thefine cellulose fiber dispersion liquid according to the fifteenthaspect, characterized in that the organic alkali is either an amine oran organic onium compound having a hydroxide ion as a counter ion.

A seventeenth aspect of the invention is the manufacturing method of thefine cellulose fiber dispersion liquid according to the fifteenthaspect, characterized in that the organic alkali is a quaternaryammonium compound having a hydroxide ion as a counter ion.

An eighteenth aspect of the invention is the manufacturing method of thefine cellulose fiber dispersion liquid according to the fifteenthaspect, characterized in that the water-based medium is either water ora mixed liquid containing water and an alcohol, and the alcohol ismethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, or 2-butanol.

A nineteenth aspect of the invention is the manufacturing method of thefine cellulose fiber dispersion liquid according to the fifteenthaspect, characterized in that the water-based medium contains awater-soluble organic solvent, and the water-soluble organic solvent isat least one organic solvent selected from the group consisting ofmethanol, ethanol, 2-propanol, acetone, methyl ethyl ketone,1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide,N,N-dimethylacetamide, dimethylsulfoxide, acetonitrile, and ethylacetate.

A twentieth aspect of the invention is the manufacturing method of thefine cellulose fiber dispersion liquid according to the fifteenthaspect, characterized by further including a preparation process to beperformed after the dispersion process by adding a water-soluble organicsolvent to the obtained fine cellulose fiber dispersion liquid, thewater-soluble organic solvent being at least one organic solventselected from the group consisting of methanol, ethanol, 2-propanol,acetone, methyl ethyl ketone, 1,4-dioxane, tetrahydrofuran,N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide,acetonitrile, and ethyl acetate.

Advantageous Effects of Invention

The present invention allows to obtain a homogeneous fine cellulosefiber dispersion liquid by effectively utilizing a cellulose, which is anatural resource having a biodegradability and causing a lowenvironmental load in a waste treatment process.

The fine cellulose fiber dispersion liquid obtained according to thepresent invention makes it possible to produce a cellulose film having ahigh heat resistance, a low linear expansion coefficient, a high elasticmodulus, a high strength, a high transparency, and an improved waterresistance. The cellulose film may be applied in a packing material(particularly, gas barrier material), a structure, a display part, orthe like. In addition, the cellulose film may be preferably applied inan electronic component having no preference for contamination ofmetal-ions such as a sodium ion, because the cellulose film is preparedwithout using any inorganic alkalis which are conventionally used in adispersion treatment process. In addition, the fine cellulose fiberdispersion liquid may be used as a coating agent or an additive agent tomake uniform complexes with various resins.

In addition, a fine cellulose fiber dispersion liquid which allows toform a film as an undercoat of a film base material, particularly a basematerial formed from a naturally occurring material such as polylacticacid, the adhesiveness of the film to the base material being improved,is provided according to the present invention. In other words, it ispossible to form various types of a functional material coating film,such as a gas barrier layer or a water vapor barrier layer, on the basematerial with favorable coatability and adhesiveness to provide alaminate body having the functional material coating film.

DESCRIPTION OF EMBODIMENTS

In the following, an aspect of a fine cellulose fiber dispersion liquidaccording to the present invention will be explained.

The fine cellulose fiber dispersion liquid of the aspect is prepared bythe following method, for example. First, a carboxyl group is introducedinto a cellulose used as a raw material.

(Raw Material)

A naturally occurring cellulose having a type I cellulose crystallinestructure may be used as a raw material. Examples of the naturallyoccurring cellulose as a raw material include a wood pulp, a non-woodpulp, a cotton cellulose, a bacterial cellulose, and a hoya cellulose.

(Oxidation Process)

There are no particular limitations on a method for oxidizing thecellulose, and the method may be arbitrarily selected depending on theintended purpose thereof, provided that a carboxyl group is introducedinto the cellulose, used as a raw material, by the method. For example,the method may be arbitrarily selected from conventionally-known methodsfor oxidizing a hydroxyl group into a carboxylic acid through analdehyde. Among the above, a method in which a nitroxy radicalderivative is used as a catalyst and a hypohalous acid salt, a halousacid salt, or the like, is used as a cooxidant is preferable.Particularly, a TEMPO (2,2,6,6-tetramethylpiperidinoxy radical)oxidation method in which an oxidation is carried out using TEMPO as acatalyst in a water-based medium containing both sodium hypochlorite andsodium bromide under an alkaline condition, preferably within the pHrange of 9 to 11, is preferable from standpoints of the easiness toobtain reagents, cost, reaction stability, selectivity to microfibrilsurface, and efficient introduction of a carboxyl group. It ispreferable in the TEMPO oxidation method that the pH in the system bemaintained at a constant level by adding an alkali aqueous solution, asneeded, because alkalis are consumed as the reaction proceeds.

In the TEMPO oxidation, a hydroxyl group at the 6-position of a pyranosering (glucose) of a cellulose molecule is selectively oxidized, as aresult of which a carboxyl group is introduced via an aldehyde group. Inthe TEMPO oxidation in which a natural cellulose is used, only thesurface of crystalline microfibrils, which are constituent units of thecellulose, is oxidized, and the inside of the crystals is not oxidized.Accordingly, it is possible to obtain a fine cellulose fiber whilemaintaining a type I cellulose crystalline structure, and the thusobtained fine cellulose fiber has a high heat resistance, a low linearexpansion coefficient, a high elastic modulus, a high strength, a gasbarrier property, and the like.

Commercially available reagents may be easily used for the TEMPOoxidation. The reaction temperature is preferably 0° C. to 60° C., andan adequate amount of the carboxyl group can be introduced forapproximately 1 to 12 hours to obtain a fine fiber exhibiting adispersibility.

The TEMPO and the sodium bromide may be used in an amount sufficient toserve as catalysts at the reaction, and may be recovered after thereaction. A theoretical by-product produced in the above-mentionedreaction system is only sodium chloride, and therefore a process fortreating waste liquid is easy and the environmental load is small.

The content of the carboxyl group may be adjusted by arbitrarily settingconditions of the TEMPO oxidation. Since cellulose fibers disperse in awater-based medium due to the action of the electronic repulsion forceof the carboxyl groups, an extremely small content of the carboxylgroup: prevents the cellulose fibers from stably dispersing in thewater-based medium; makes it difficult for the cellulose fiber to formuniform complexes with various resins when a dispersion liquid thereofis used as a coating agent or an additive agent; and deteriorates acoatability and a gas barrier property thereof. An extremely largecontent of the carboxyl group increases the affinity for water, whichlowers the water resistance or the crystallinity, and thereby weakeningthe strength and deteriorating the gas barrier property. In view of theabove-mentioned matters, the content of the carboxyl group is preferably0.1 mmol/g to 3.5 mmol/g, more preferably 0.1 mmol/g to 2 mmol/g, andeven more preferably 0.6 mmol/g to 2 mmol/g. In the process ofintroducing a carboxyl group, an aldehyde group is formed as anintermediate of the oxidation reaction, and the aldehyde group remainsin the final product. Since an extremely large content of the aldehydegroup lowers the dispersibility in the water-based medium, the contentof the aldehyde group is preferably 0.01 mmol/g to 0.3 mmol/g.

The oxidation reaction is ended by adding an excess amount of anotheralcohol to completely consume the cooxidant in the system. It isdesirable to use a low-molecular weight alcohol, such as methanol,ethanol, or propanol, as the alcohol to be added, in order to promptlyend the reaction. Among these, ethanol is preferable, taking intoaccount the safety and by-products produced by oxidation.

(Recovery of Oxidized Cellulose)

After the end of the oxidation reaction, the resulting oxidizedcellulose may be recovered from the reaction liquid by filtration. Inthe oxidized cellulose obtained after the end of the reaction, thecarboxyl group forms a salt with a metal-ion, as a counter ion thereof,derived from the cooxidant or an inorganic alkali for adjusting the pH.Examples of the recovery method include: a method in which filtrationand separation are performed while keeping the carboxyl group formingthe salt; a method in which the pH of the reaction liquid is adjusted to3 or less by adding an acid thereto to obtain a carboxylic acid,followed by performing filtration and separation; and a method in whichan organic solvent is added to form an agglomerate, followed byperforming filtration and separation. Since the majority of the counterion (metal-ion) in the oxidized cellulose is removed once the salt isconverted to a carboxylic acid, filtration and separation are performedafter the conversion to the carboxylic acid. The method in which therecovery is performed after the conversion to the carboxylic acid ispreferable taking into account the handling ability, the yield, and thewaste liquid treatment. The conversion to the carboxylic acid allows foran efficient washing with water, a decreased metal-ion content, and areduced number of washing steps.

The metal-ion content in the oxidized cellulose may be determined byvarious analysis methods, and, for example, may be easily determined byan EPMA method using an electron beam micro analyzer, or an elementalanalysis of a fluorescent X-ray analysis method. Whereas the metal-ioncontent ratio is 5% by weight or more when recovered by performingfiltration and separation with keeping the salt formed, the metal-ioncontent ratio is 1% by weight or less when recovered by performingfiltration and separation after the conversion to a carboxylic acid.

(Washing)

The recovered oxidized cellulose may be purified by repeating washing,and thereby removing residues such as catalysts, salts, and ions. At thewashing steps, water is preferably used as a washing liquid, andwater-washing performed after washing under an acidic condition in whichthe pH is adjusted to 3 or less, more preferably 1.8 or less, using ahydrochloric acid, makes the metal-ion content less than or equal to theminimum detectable quantity by the above-mentioned analysis method. Thewashing step performed under the acidic condition may be repeatedlyperformed in order to further reduce the remaining metal-ion content. Itis preferable that the water-washing step be repeatedly performed,because the presence of remaining salts and the like in the cellulosedmakes dispersion difficult at a dispersion process mentioned below.

Next, processes for preparing a fine cellulose fiber dispersion liquidusing the oxidized cellulose obtained by the above-mentioned procedureswill be explained.

(Dispersion Process)

First, the washed oxidized cellulose is immersed in a water-based mediumas a dispersion medium in a pulverizing process of the oxidizedcellulose. It is preferable in the process that water or a mixed liquidcontaining water and an alcohol be used as the water-based medium.Examples of the alcohol to be used include methanol, ethanol,1-propanol, 2-propanol, 1-butanol, and 2-butanol. At least one type ofthe organic solvents may be mixed.

In the process, an existence of the alcohol-based substance in themedium allows for a further homogeneous dispersion when an organicsolvent is further added after a dispersion process. In addition, it ispossible to improve the temporal stability of a dispersion liquid.Although an additive amount of the alcohol is not particularly limited,the additive amount is preferably 1% to 60%, more preferably 1% to 50%,and even more preferably 1% to 20%, with respect to an amount of water.When the alcohol is contained, the coatability of the dispersion liquidused as a coating agent or an additive agent is improved, and the dryingenergy thereof is reduced in comparison with that of water alone.

In the process, the pH of the liquid for immersion is, for example, 4 orless. The oxidized cellulose is insoluble in the water-based medium, andforms a heterogeneous suspension when immersed.

A dispersion medium consisting of an alcohol, free from water, may alsobe used to prepare the fine cellulose fiber dispersion liquid.

The water-based medium may contain, in addition to either water or themixed liquid of water and the alcohol, a water-soluble organic solventwhich can be uniformly mixed with water. Examples of the water-solubleorganic solvent to be used include: the above-mentioned alcohols, suchas methanol, ethanol, and 2-propanol (IPA); ketones such as acetone, andmethyl ethyl ketone (MEK); ethers such as 1,4-dioxane andtetrahydrofuran (THF); N,N-dimethylformamide (DMF),N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetonitrile,and ethyl acetate. These may be used alone or as a mix solvent of atleast two types thereof. In the case where a mixed solvent of water andthe water-soluble organic solvent is used as the water-based medium, themixing ratio thereof may be arbitrarily determined taking into accountthe type of the water-soluble organic solvent, the affinity betweenwater and the water-soluble organic solvent, and the like.

Next, the pH of the suspension is adjusted to 4 to 12 using an alkali.In particular, the pH is adjusted to an alkaline region of 7 to 12 toform a carboxylic acid salt. As a result, an electronic repulsionbetween the carboxyl groups is readily generated, and thereby thedispersibility is improved and it becomes easy to obtain the finecellulose fiber. Although a mechanical dispersion treatment makes itpossible to pulverize the cellulose into fine fibers even at the pH ofless than 4, the dispersion treatment requires a further long-term andhigh-energy, the thus obtained fiber has a fiber diameter larger thanthat of the present invention, and the thus obtained fine cellulosefiber dispersion liquid has a poor transparency.

An ammonia water or an organic alkali is used as the alkali to adjustthe pH in order to prevent the fine cellulose fiber dispersion liquidfrom accompanying metal-ions. An amount of the alkali added, which isless than or equal to the content of the carboxyl group in molar ratio,is sufficient, and an even amount of the alkali added, which is lessthan or equal to two-thirds of the content of the carboxyl group, allowsfor a dispersion. It is not preferable that the amount of the alkaliadded be extremely large, because coloration of the dispersion liquidoccurs. Examples of the organic alkali include: various amines, such asaliphatic amines, aromatic amines, and diamines; and organic oniumcompounds having a hydroxide ion as a counter ion, such as: ammoniumhydroxide compounds represented by NR₄OH (in which R represents an alkylgroup, a benzyl group, a phenyl group, or a hydroxyalkyl group, and fourR may be the same or different from each other), such as tetramethylammonium hydroxide, tetraethyl ammonium hydroxide, tetra-n-butylammonium hydroxide, benzyltrimethyl ammonium hydroxide, 2-hydroxyethyltrimethyl ammonium hydroxide; phosphonium hydroxide compounds such astetraethyl phosphonium hydroxide; oxonium hydroxide compounds, andsulfonium hydroxide compounds. In the case where the organic alkali isused, the fiber may be pulverized, without depending on the type of thealkali, by subjecting to the dispersion treatment at a level less thanor equal to that to be performed using an inorganic alkali. Inparticular, in the case where the organic alkali is used, the bulkinessthereof promotes the dispersion due to the microfibril repulsion of thecellulose. In addition, there is a case where the viscosity of thedispersion liquid is lowered, which allows for an efficient dispersion.

The fine cellulose fiber obtained using the organic alkali improves thewater resistance of a cellulose film and a cellulose coating filmmentioned below due to the hydrophobicity of the organic alkali.

In addition, even if an alcohol is used as a water-based medium, the useof the organic alkali makes it possible to prepare a uniformly-dispersedfine cellulose fiber dispersion liquid due to the high affinity of theorganic alkali for the alcohol. In addition, the use of the organicalkali is effective, because such a use prevents the dispersed finecellulose fiber dispersion liquid from agglomerating, getting clouded,and becoming heterogeneous, even if a water-soluble organic solventmentioned below is added to the fine cellulose fiber dispersion liquidsubjected to the dispersion treatment in the water-based medium.

In addition, in the case where the organic alkali is used as an alkali,the dispersion treatment requires less energy and less time, incomparison with the case where an inorganic alkali having a metal-ion asa counter ion is used as an alkali. In addition, the transparency of thefine cellulose fiber dispersion liquid finally obtained can be improved.The reason for the above is considered to be that the use of the organicalkali has a larger effect of separating the fine cellulose fibers fromeach other in the dispersion medium due to a larger ion size of acounter ion of the organic alkali than that of the other.

In addition, the fine cellulose fiber dispersion liquid generallybecomes gelatinous and the viscosity thereof increases as theconcentration thereof increases, and, therefore, a dispersion treatmentrequires a large amount of energy, which makes the dispersion treatmentdifficult. In comparison with the case in which an inorganic alkali isused, the use of an organic alkali is favorable because both theviscosity and the thixotropy of the dispersion liquid decrease, and bothdispersion treatment and coating treatment at a coating processmentioned below become easy. Although the fine cellulose fiberdispersion liquid generally becomes gelatinous and the viscosity thereofincreases as the concentration thereof increases, and, therefore, alarge amount of energy is required at the dispersion treatment and thedispersion treatment becomes difficult, the viscosity of the dispersionliquid is lowered by using an organic alkali, and the dispersiontreatment becomes easy. In addition, the use of the organic alkali witha water-soluble organic solvent mentioned below makes it possible tocontrol the viscosity property of the dispersion liquid, and therebyimproving the coatability thereof.

The thus prepared fine cellulose fiber dispersion liquid contains: afine cellulose fiber having a carboxyl group; and either an amine or anorganic onium ion derived from the organic alkali. The fine cellulosefiber dispersion liquid is isolated, dried, filtered, and separated, inaccordance with conventionally-known procedures, to obtain a finecellulose fiber having a carboxyl group with either an amine or anorganic onium ion as a counter ion.

Examples of the organic onium ion include onium ions, cations of theabove-mentioned organic alkali, such as a quaternary ammonium ion, aquaternary phosphonium ion, a tertiary oxonium ion, and a tertiarysulfonium ion. In the case where a phosphonium ion is the counter ion,the heat resistance is improved, and the compatibility between the oniumion and a resin can be regulated.

On the other hand, the use of an inorganic alkali such as sodiumhydroxide makes the pulverization in the solvent or mixing with thesolvent difficult. In the case where a water-soluble organic solvent isadded to the fine cellulose fiber dispersion liquid prepared using theinorganic alkali containing a metal-ion, the dispersed fine cellulosefibers are agglomerated, and therefore the fine cellulose fiberdispersion liquid is agglomerated, gets clouded, and becomesheterogeneous. The fact becomes a problem to deteriorate the coatabilityof the dispersion liquid used as a coating agent, and lower themechanical strength, the transparency, and the barrier properties, of aformed film or laminated material, when the water-soluble organicsolvent mentioned below is added to obtain a predetermined viscosity orsolid content concentration of the fine cellulose fiber dispersionliquid for forming the film or the laminated material using the finecellulose fiber dispersion liquid.

Conventionally-known various dispersion methods may be adopted toperform dispersion treatment in the water-based medium. Examples thereofinclude treatment with a homomixer, treatment with a mixer equipped witha rotary blade, treatment with a high-pressure homogenizer, treatmentwith an ultrahigh-pressure homogenizer, treatment with an ultrasonichomogenizer, treatment with a nanogenizer, treatment with a diskrefiner, treatment with a conical refiner, treatment with a double diskrefiner, treatment with a grinder, treatment with a ball mill, andunderwater opposite treatment. Among the above-mentioned treatments, thetreatment with a mixer equipped with a rotary blade, the treatment witha high-pressure homogenizer, the treatment with an ultrahigh-pressurehomogenizer, and the treatment with an ultrasonic homogenizer arepreferable from the standpoint of pulverizing efficiency. At least twoof the treatment methods may be adopted to perform dispersion.

The above-mentioned dispersion treatment makes the suspension a visuallyhomogeneous and transparent dispersion liquid. The oxidized cellulose ispulverized by the dispersion treatment to be a fine cellulose fiber.

The fine cellulose fiber after the dispersion treatment preferably has anumber-average fiber diameter (width in a short axis direction of thefiber) of 0.001 μm to 0.200 μm, more preferably 0.001 μm to 0.050 μm.The fiber diameter of the fine cellulose fiber may be determined using ascanning electron microscope (SEM) or an atomic force microscope (AFM).If the dispersion is insufficient and heterogeneous and thereforecellulose fibers having a large fiber diameter (a number-average fiberdiameter of which exceeds 0.200 μm) are contained, problems occur inwhich: the coatability of the dispersion liquid containing the finecellulose fiber deteriorates; and the transparency, the smoothness, andthe gas barrier property of formed film significantly deteriorate. Inaddition, uniform dispersion becomes difficult when the dispersionliquid is mixed with other materials as an additive agent.

In the case where the organic alkali is used as an alkali, it ispreferable that the transmittance of the obtained fine cellulose fiberdispersion liquid be at least 90% when the solid content concentrationthereof is 0.5%. If the transmittance of the obtained fine cellulosefiber dispersion liquid is at least 90%, the fine cellulose fiberdispersion liquid can form a cellulose film or a laminated materialhaving a sufficient transparency. In particular, it is more preferablethat the transmittance of the obtained fine cellulose fiber dispersionliquid be at least 97% when the solid content concentration thereof is0.5%.

(Preparation Process)

A water-soluble organic solvent may be further added to the finecellulose fiber dispersion liquid obtained by dispersion treatment. Thewater-soluble organic solvent to be added to the fine cellulose fiberdispersion liquid may be any organic solvent which is soluble in water,and examples thereof include the above-mentioned water-soluble organicsolvents to be contained in the water-based medium in the dispersionprocess, such as: alcohols such as methanol, ethanol, and 2-propanol;ketones such as acetone, and methyl ethyl ketone (MEK); ethers such as1,4-dioxane, and tetrahydrofuran (THF); N,N-dimethylformamide (DMF),N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetonitrile,and ethyl acetate. The process is useful to form a composite materialwith a resin, because the solubility of the resin is enhanced.

The above-mentioned water-soluble organic solvents may be used alone, orin combination of at least two types thereof. In addition, theabove-mentioned water-soluble organic solvent may be used in combinationwith water.

Although an amount of the water-soluble organic solvent to be added maybe determined taking into account the type thereof, it is preferablethat the minimum amount thereof be 0.1% by weight, and the maximumamount thereof be 60% by weight, with respect to the total amount of thefine cellulose fiber dispersion liquid. However, in the case where thewater-soluble organic solvent has a relatively-large affinity for water,such as alcohols or acetone, the maximum additive amount thereof may be,for example, approximately 99.9% by weight, as needed. On the otherhand, in the case where the water-soluble organic solvent has arelatively-small affinity for water, the maximum additive amount thereofmay be approximately 50% by weight, as needed.

If the additive amount of the water-soluble organic solvent is less than0.1% by weight, improvements in: the solubility of the resin; the dryingefficiency mentioned below; and the coatability of the fine cellulosefiber dispersion liquid are insufficient. On the other hand, theadditive amount of the water-soluble organic solvent is preferably atleast 10% by weight, more preferably at least 30% by weight, becauseimprovements in: the solubility of the resin; the drying efficiencymentioned below; and the coatability of the fine cellulose fiberdispersion liquid are sufficient.

In the case where multiple types of the water-soluble organic solventare used in combination or both the water-soluble organic solvent andwater are used in combination, the mixing ratio thereof may bearbitrarily determined taking into account the solid contentconcentration or the viscosity of the fine cellulose fiber dispersionliquid, or properties required for a film or a laminated material formedusing the fine cellulose fiber dispersion liquid.

As mentioned above, the water-soluble organic solvent may be used as thedispersion medium, that is, the water-based medium, for the oxidizedcellulose at the dispersion process or may be used as an organic solventto be added to the fine cellulose fiber dispersion liquid obtained bythe dispersion process without being used as the water-based medium.

Specific examples of the process include: (1) a method in which theoxidized cellulose suspension is subjected to the dispersion treatmentusing water alone as the water-based medium to obtain the fine cellulosefiber dispersion liquid, followed by adding the water-soluble organicsolvent to the obtained fine cellulose fiber dispersion liquid; and (2)a method in which the oxidized cellulose suspension is subjected to thedispersion treatment using a mixed solvent composed of water and awater-soluble organic solvent as the water-based medium to obtain thefine cellulose fiber dispersion liquid. In the method (2), thewater-soluble organic solvent which is the same or different from oneused as the water-based medium may be added to the obtained finecellulose fiber dispersion liquid. The methods (1) and (2) are oneaspect of the present invention, and the present invention is notlimited to the aspect.

The addition of the water-soluble organic solvent to the fine cellulosefiber dispersion liquid obtained by performing the dispersion treatmentreduces the surface tension of the fine cellulose fiber dispersionliquid and improves the wettability with respect to the base material.In particular, a solvent having a high solubility of the base materialis preferably used as the water-soluble organic solvent. Although, inthe case where a polylactic acid is used as the base material, thesurface of the base material after coating is slightly eroded, andthereby improving the adhesiveness, for example, poorly-solublemethanol, ethanol, 2-propanol (IPA), or the like, is preferable, andacetone, methyl ethyl ketone (MEK), tetrahydrofuran (THF), ethylacetate, or the like, is more preferable. The adhesion mechanism isconsidered to be that the organic solvent erodes the surface of the basematerial, and the coating liquid of the fine cellulose fiber dispersionliquid enters therein to adhere thereto.

The fine cellulose fiber exhibits effects of suppressing the thermalshrinkage of the base material when coated on the base material as acoating film, due to the high crystallinity and the small linearexpansion coefficient thereof. In the case where a laminate bodymentioned below is formed, although the difference in the linearexpansion coefficient between a base material and a functional materialcauses a problem of boundary separation therebetween when heating at adrying or forming step, the formation of the coating film containing thefine cellulose fiber on the base material suppresses shrinkage of thebase material, and thereby preventing separation from the base material.

A compound having a reactive functional group, such as an amino group,an epoxy group, a hydroxyl group, a carbodiimide group, apolyethylenimine, an isocyanate, an alkoxy group, a silanol group, or anoxazoline group, may be added as an additive agent to the fine cellulosefiber dispersion liquid. The additive agent reacts with a hydroxylgroup, a carboxyl group, or an aldehyde group, in the oxidizedcellulose, and thereby exhibiting effects of improving variousproperties of the coating film, particularly, the film strength thereof,the water resistance thereof, the moisture resistance thereof, or theadhesiveness thereof to the base material.

Examples of the compound having a silanol group include silane couplingagents, alkoxysilanes, and hydrolysates thereof. The silane couplingagents are silane compounds having at least two hydrolyzable groupsbinding to a silicon atom.

The hydrolyzable groups are groups hydrolysable to hydroxyl groups. Whenhydrolyzation occurs, a silanol group (Si—OH) is generated in the silanecoupling agent.

Examples of the hydrolyzable group include an alkoxy group, an acetoxygroup, and a chlorine atom, and an alkoxy group is preferable among theabove. That is, an alkoxysilane is preferable as the silane couplingagent. An alkyl group of the alkoxy group is preferably an alkyl grouphaving 1 to 5 carbon atoms, more preferably a methyl group or an ethylgroup, and particularly preferably an ethyl group.

In the case where the silane coupling agent has two or threehydrolyzable groups, it is preferable that the silane coupling agentfurther has another reactive functional group.

As the reactive functional group, ones which can form a chemical bond(covalent bond) or interact with each other (form a hydrogen bond) dueto the reaction with a functional group (such as a carboxy group or ahydroxyl group) present on the cellulose nanofiber surface or the basematerial surface may be arbitrarily selected from functional groups oforganic groups binding to a Si atom of generally-used silane couplingagents. Specific examples thereof include a vinyl group, an epoxy group,a methacryloxy group, an acryloxy group, an amino group, an ureidogroup, a mercapto group, a chlorine atom, and an isocyanate group. Amongthe above, an epoxy group, a methacryloxy group, an acryloxy group, andan amino group are preferable, and an amino group is particularlypreferable.

In the case where the reactive compound, particularly the compoundhaving an alkoxy group and a silanol group, is used to enhance theeffects of improving various properties of the coating film,particularly, the film strength thereof, the water resistance thereof,the moisture resistance thereof, or the adhesiveness thereof to the basematerial, homogeneous mixing is important. In particular, the finecellulose fiber dispersion liquid according to the present invention ispreferable in terms of the low viscosity thereof, the mixability thereofwith the alcohol, the absence of metal-ions such as a sodium ion, andability to suppress reactive agglomeration and heterogeneous reaction.In addition, an inorganic layered compound may be added as an additiveagent.

The inorganic layered compound is a crystalline inorganic compoundhaving a layered structure, and examples thereof include clay mineralsas typified by the kaolinite family, the smectite family, the micafamily, and the like. The inorganic layered compound may be arbitrarilyselected depending upon required properties thereof without beingparticularly limited on the types thereof, the synthetic or naturalorigin thereof, the production area thereof, the particle diameterthereof, the aspect ratio thereof, or the like. General examples of theinorganic layered compound of the smectite family includemontmorillonite, hectorite, saponite, and the like. Among the above,montmorillonite is preferable in terms of the stability thereof in thecoating liquid, the coatability thereof, and the like. The addition ofthe inorganic layered compound particularly improves the gas barrierproperty.

The obtained fine cellulose fiber may be mixed with a resin such as anepoxy resin, a polyester resin, an acrylic resin, an urethane resin, apolyolefin resin, a polyimide resin, or a polyamide resin, to prepare acomposite composition. In addition, the composite composition may beused to prepare a composite material which is homogeneous andtransparent. The composite composition effects on improving themechanical strength of the obtained composite material, lowering thelinear expansion coefficient thereof, and enhancing the elastic modulusthereof.

In particular, the use of the above-mentioned water-based resin makes itpossible to prepare a more homogeneous composite composition which canform a composite material: having a high fiber dispersibility; andexhibiting improved effects mentioned above. The use of theabove-mentioned emulsion-based resin to form a composite compositionmakes it possible to lower the drying energy, improve the dispersibilityand stability of the emulsion, prevent there-agglomeration/precipitation, and form a complex with various resins.

The composite composition may contain, as needed, various additiveagents, such as a silane coupling agent, a leveling agent, anantifoamer, an inorganic particle, an organic particle, a lubricantagent, an antistatic agent, an ultraviolet absorber, a pigment, a dye, alight stabilizer, an antioxidant, a plasticizer, a flame retardant, adispersing agent, a foaming agent, or a filler, in addition to the finecellulose fiber and the resin.

Examples of the composite material prepared using the compositecomposition include a dye, an ink, a transparent base material, a filmbase material, a compact, a container, a chassis, and an electroniccomponent. Among the above, the preferable use of the composite materialprepared using the composite composition is a transparent base material,taking into account an improved mechanical strength, lowered linearexpansion coefficient, and enhanced elastic modulus, which are caused byusing the composite composition.

The fine cellulose fiber dispersion liquid according to the presentinvention allows for a uniform dispersion to form a complex withoutcausing agglomeration or precipitation even if the fine cellulose fiberdispersion liquid is added to a solvent-free or solvent-based resininstead of the water-based resin.

Next, a cellulose film and a laminate body, prepared using the finecellulose fiber dispersion liquid according to the present invention,will be explained.

(Cellulose Film)

The fine cellulose fiber dispersion liquid according to the presentinvention may be used as a material for forming a self-supporting filmof a cellulose film by a method in which a cast process is performed orthe fine cellulose fiber dispersion liquid is coated or extruded on thebase material to form a film, followed by drying and separating thefilm. Since the fine cellulose fiber dispersion liquid according to thepresent invention contains the organic alkali, it is possible to lowerthe viscosity of the fine cellulose fiber dispersion liquid and increasethe solid content concentration thereof to at least 2%. Thus, it ispossible to use the fine cellulose fiber dispersion liquid inhighly-concentrated form, and therefore a thick film base material canbe easily prepared.

It is preferable that the fine cellulose fiber dispersion liquid containthe mixed solvent containing water and the water-soluble organicsolvent, in terms of decreasing the drying energy. As the water-solubleorganic solvent to be used, a low-molecular weight alcohol, such asmethanol, ethanol, 1-propanol, or 2-propanol, or a ketone, such asacetone or methyl ethyl ketone, is particularly preferable, taking intoaccount the cost or boiling point thereof. The formed cellulose film isexpected to be applied to an insulating film or an electrolyte film of afuel cell or a display part.

In the case where the fine cellulose fiber dispersion liquid containsthe mixed solvent containing water and the alcohol, the dispersionmedium hardly remains in the dried coating film, which results in adense film, and therefore the mechanical strength and the waterresistance of the film are improved.

(Laminate Body)

The fine cellulose fiber dispersion liquid may be coated on the basematerial by a conventionally-known coating process, such as, a gravurecoating process, a reverse gravure coating process, a roll coatingprocess, a reverse roll coating process, a microgravure coating process,a comma coating process, an air-knife coating process, a bar coatingprocess, a Mayer bar coating process, a dip coating process, a diecoating process, a spray coating process, a slit coating process, or ascreen printing process, to form a laminate body.

The base material is not particularly limited, and may be arbitrarilyselected as usage thereof from conventionally-used various basematerials in a sheet form (including a film form). The base material maybe made, for example, from a paper, a paper board, a biodegradableplastic, such as polylactic acid or polybutyl succinate, apolyolefin-based resin (such as polyethylene or polypropylene), apolyester-based resin (such as polyethylene terephthalate,polybutyleneterephthalate or polyethylene naphthalate), apolyamide-based resin (such as nylon-6 or nylon-66), a polyvinylchloride-based resin, a polyimide-based resin, or a copolymer of atleast two of monomers forming the polymers. The base material maycontain a conventionally-known additive agent such as an antistaticagent, an ultraviolet absorber, a plasticizer, a lubricant, or acoloring agent.

The base material, particularly, made from a paper, a biodegradableplastic such as polylactic acid or polybutyl succinate, or a biomassmaterial such as bio-polyethylene, is preferably used, becauseadvantages of the fine cellulose fiber derived from the natural productwith a small environmental burden are maximally exhibited.

The surface of the base material may be subjected to surface treatmentsuch as corona treatment, plasma treatment, ozone treatment, or frametreatment. The surface treatment further improves the wettability or theadhesiveness of the base material surface with respect to the layer tobe laminated thereon (the layer having the fine cellulose fiberdispersion liquid). The surface treatment may be performed by aconventionally-known method.

The thickness of the base material may be arbitrarily determined asusage of the laminate body. In the case where the laminate body is usedas a packing material, for example, the thickness thereof is generally10 μm to 200 μm, preferably 10 μm to 100 μm.

A coating film of the fine cellulose fiber dispersion liquid is driedwith an oven or the like, to form a coating film of the fine cellulosefiber on the base material. At the process, it is preferable that thefine cellulose fiber dispersion liquid contain a mixed solventcontaining water, an alcohol, and the like, in order to decrease thesurface tension of the coating film to improve the wettability thereofwhile preventing occurrence of eye holes at a coating process, as wellas to reduce the drying energy thereof. In addition, the mechanicalstrength and the gas barrier property of the coating film are alsoimproved, due to the same reasons as those mentioned above. The alcoholis preferably the low-molecular weight alcohol mentioned above.

The fine cellulose fiber dispersion liquid may be used as a bonding-,anchor-coating-, or primer-composition containing both the finecellulose fiber and the organic solvent. In particular, the finecellulose fiber dispersion liquid is used by coating on the basematerial such as polylactic acid to form a biomass film having anexcellent coatability and adhesiveness with respect to the basematerial.

The fine cellulose fiber dispersion liquid may be used, for example, toform a film as an undercoat layer (first coating film layer), followedby laminating a functional material layer (second coating film layer)formed using a functional material, such as a gas-barrier materialmentioned below, an ink, or the like, to form a functional laminate bodyhaving a high adhesiveness with respect to the base material. Thefunctional material layer may be formed on the fine cellulose fiber filmby the above-mentioned known coating or printing method.

In particular, in the case where the functional material layer is formedusing a coating liquid containing the fine cellulose fiber, thefunctional material layer has a high affinity for the undercoat layerformed using the fine cellulose fiber dispersion liquid, has no eyehole, and exhibits a favorable adhesiveness with respect to theundercoat layer.

In addition, various functional material layers, such as a thermaladhesive thermoplastic resin layer, a printing layer, an adhesive layer,an antistatic layer, an antireflective layer, an antidazzle layer, apolarization layer, a phase-contrast layer, a scratch-resistant- orantifoulant-protection layer, a vapor-deposited layer, a gas barrierlayer against oxygen or the like, a water vapor barrier layer, a drugbarrier layer, an adsorbent layer, a catalyst layer, or the like, may beformed on the above-mentioned cellulose film or laminate body, asneeded.

Among the functional material layers mentioned above, a vapor-depositedlayer particularly has an effect of improving the gas barrier property.

Inorganic compounds for forming the vapor-deposited layer are notparticularly limited, and ones conventionally used to form avapor-deposited film of a gas barrier material or the like. Specificexamples thereof include inorganic oxides such as aluminum oxide,magnesium oxide, silicon oxide, and tin oxide. The inorganic compoundsmay be used alone, or in combination of at least two types thereof.

The optimum thickness of the vapor-deposited layer varies depending onthe type or composition of the inorganic compounds, and is arbitrarilyselected from a range of several nm to 500 nm, preferably 5 to 300 nm,taking into account the desired gas barrier property, or the like, ingeneral. If the thickness of the vapor-deposited layer is extremelythin, the sequentially of the vapor-deposited film is not maintained,while if the thickness thereof is extremely thick, the flexibilitythereof is lowered, and thereby easily generating cracks, and thereforethe gas barrier property of the vapor-deposited layer may not besufficiently exhibited.

The vapor-deposited layer may be formed by a conventionally-known methodsuch as a vacuum vapor deposition method, a sputtering method, a plasmavapor phase growth method (CVD method), or the like, alternatively or acommercially available film or sheet having a vapor-deposited layerformed thereon may be used as the base material.

Among the above-mentioned functional material layers, a thermal adhesivethermoplastic resin layer is useful as a packing material, becauseprocessing, sealing, or the like, can be done by heat-sealing. Examplesof the thermal adhesive thermoplastic resin layer include polypropylenefilm such as unstretched polypropylene film (CPP), polyethylene filmsuch as low-density polyethylene film (LDPE), or straight-chainlow-density polyethylene film (LLDPE), and the like.

The thermoplastic resin layer is generally laminated on the cellulosefilm or the laminate body by extruding or using an adhesive agent layertherebetween.

EXAMPLES

Next, the present invention is described in more specific, based on aseries of examples. However, the present invention is in no way limitedby the examples.

(Preparation of Oxidized Cellulose)

A bleached pulp of a needle-leaved tree commonly available was used as acellulose.

30 g of the cellulose (calculated in terms of the absolute dry massthereof) was added to 600 g of distilled water and then stirred to beswollen, followed by fibrillating using a mixer. A solution composed of1200 g of distilled water, 0.3 g of TEMPO previously dissolved in 200 gof distilled water, and 3 g of sodium bromide was added to theresultant, and 86 g of an aqueous solution containing 2 mol/L of sodiumhypochlorite was added dropwise thereto to start oxidation reaction. Thereaction temperature was always maintained at 20° C. or lower. Althoughthe pH in the system during the reaction lowered, the pH was adjusted to10 by gradually adding thereto an aqueous solution containing 0.5 N ofNaOH. The reaction was stopped by adding 30 g of ethanol 3 hours afterthe reaction proceeded. Then, 0.5 N of HCl was added dropwise to thereaction liquid to lower the pH to 1.8. The reaction liquid was filteredusing a nylon mesh, followed by washing the solid content using waterseveral times to remove the reaction reagents or by-products, andthereby obtaining an oxidized cellulose containing water, the solidcontent concentration of the resultant being 7%.

(Measurement of the Introduction Amount of Functional Groups)

0.2 g of the moist oxidized cellulose, calculated in terms of theabsolute dry mass thereof, was put into a beaker, and distilled waterwas added thereto to amount to 60 g. 0.5 mL of an aqueous solutioncontaining 0.1 M of NaCl was added thereto, and the pH of the resultantwas adjusted to 1.8 using 0.5 M of hydrochloric acid, followed by addingan aqueous solution containing 0.5 M of NaOH dropwise to measure theconductivity of the resultant. The measurement was continued until thepH of the resultant reached approximately 11. An additive amount of NaOHat the neutralization stage of the weak acid, which corresponded to thecontent of carboxyl groups, was read from the obtained conductivitycurve to determine the content of carboxyl groups to be 1.6 mmol/g.

Next, 20 mL of 0.5 M acetic acid, 60 ml of distilled water, and 1.8 g ofsodium chlorite were added to 2 g of the moist oxidized cellulose,calculated in terms of the absolute dry mass thereof, and the pH of theresultant was adjusted to 4, followed by allowing the reaction toproceed for 48 hours. Then, the content of carboxyl groups was measuredas mentioned above, which revealed that the content thereof was 1.8mmol/g. As a result, the content of aldehyde groups was calculated to be0.2 mmol/g.

Example 1 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water was added to 57.14 g (4 g in terms of solid content) ofthe oxidized cellulose prepared as mentioned above, the oxidizedcellulose having a solid content concentration of 7%, to obtain 400 g ofan oxidized cellulose suspension. The pH of the resultant was adjustedto 8 using 10% by weight of tetraethyl ammonium hydroxide (TEAHmanufactured by Kanto Kagaku Co., Ltd.). The thus prepared dispersionliquid was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid.

Example 2 Preparation of Fine Cellulose Fiber Dispersion Liquid

199 g of ethanol (EtOH) and distilled water were added to 28.57 g (2 gin terms of solid content) of the oxidized cellulose prepared asmentioned above, the oxidized cellulose having a solid contentconcentration of 7%, to obtain 400 g of an oxidized cellulosesuspension. The pH of the resultant was adjusted to 8 using 10% byweight of tetraethyl ammonium hydroxide. The thus prepared dispersionliquid was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid.

Comparative Example 1 Preparation of Fine Cellulose Fiber DispersionLiquid

Distilled water was added to 57.14 g (4 g in terms of solid content) ofthe oxidized cellulose prepared as mentioned above, the oxidizedcellulose having a solid content concentration of 7%, to obtain 400 g ofan oxidized cellulose suspension. The pH of the resultant was adjustedto 8 using an aqueous solution of sodium hydroxide (NaOH). The thusprepared dispersion liquid was treated with a mixer equipped with arotary blade for 60 minutes, to obtain a fine cellulose fiber dispersionliquid.

Comparative Example 2 Preparation of Fine Cellulose Fiber DispersionLiquid

199 g of ethanol and distilled water were added to 28.57 g (2 g in termsof solid content) of the oxidized cellulose prepared as mentioned above,the oxidized cellulose having a solid content concentration of 7%, toobtain 400 g of an oxidized cellulose suspension. The pH of theresultant was adjusted to 8 using an aqueous solution of sodiumhydroxide. The thus prepared dispersion liquid was treated with a mixerequipped with a rotary blade for 60 minutes.

(Measurement of Transmittance of the Fine Cellulose Fiber DispersionLiquid)

The fine cellulose fiber dispersion liquids prepared in Examples 1 and 2and Comparative Examples 1 and 2 were compared in terms of thetransparency thereof by measuring the transmittance thereof at 660 nmusing a spectrophotometer.

(Cellulose Film)

The fine cellulose fiber dispersion liquids prepared in Examples 1 and 2and Comparative Examples 1 and 2 were poured into square plasticcontainers, and then dried at 50° C. overnight, followed by drying at120° C. for 1 hour to obtain cellulose films.

(Measurement of the Content of Sodium Ions)

The contents of sodium ions in the cellulose films were measured by anEPMA method using an X-RAY micro analyzer.

(Swelling Test)

The cellulose films were subjected to the swelling test (N=2),respectively, by immersing the cellulose films in distilled water for 1minute to compare values of the weight thereof before and after theimmersion.

The transmittance of the fine cellulose fiber dispersion liquidsprepared in Examples 1 and 2 and Comparative Examples 1 and 2, thesodium ion content in the cellulose films, and the results of theswelling test are shown in Table 1.

TABLE 1 Example Example Comparative Comparative 1 2 Example 1 Example 2Alkali species TEAH TEAH NaOH NaOH Dispersion Water Water/ WaterWater/EtOH medium EtOH Solid content 1 0.5 1 0.5 concentration (%) pH 88 8 8 Transmittance 86.0 73.0 83.0 0.4 (%) Na content Below Below 9.27.0 (wt %) measurable measurable limits limits Swelling property 17.513.5 24.3 Deterioration Weight change (fold)

The transmittance of the fine cellulose fiber dispersion liquidsprepared in Examples 1 and 2 and Comparative Example 1 was at least 70%,while the fine cellulose fiber dispersion liquid prepared in ComparativeExample 2 was scarcely dispersed and maintained to be clouded.

No sodium ion was detected from the cellulose films prepared in Examples1 and 2 using the organic alkali.

The cellulose films prepared in Examples 1 and 2 exhibited an improvedswelling-resistance against water and a superior water resistance incomparison with those prepared in the comparative examples. Inparticular, the change in weight due to swelling was further suppressedin Example 2 in which ethanol was formulated in the dispersion medium.

Example 3 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 10% by weight of tetramethyl ammonium hydroxide(TMAH manufactured by Kanto Kagaku Co., Ltd) were added to 28.57 g (2 gin terms of solid content) of the oxidized cellulose prepared asmentioned above, the oxidized cellulose having a solid contentconcentration of 7%, to obtain 400 g of an oxidized cellulose suspensionhaving a pH of 10. The thus prepared suspension was treated with a mixerequipped with a rotary blade for 60 minutes, to obtain a fine cellulosefiber dispersion liquid.

Example 4 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 10% by weight of tetraethyl ammonium hydroxide wereadded to 28.57 g (2 g in terms of solid content) of the oxidizedcellulose prepared as mentioned above, the oxidized cellulose having asolid content concentration of 7%, to obtain 400 g of an oxidizedcellulose suspension having a pH of 10. The thus prepared suspension wastreated with a mixer equipped with a rotary blade for 60 minutes, toobtain a fine cellulose fiber dispersion liquid.

Example 5 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 0.4 mol/l of tetra-n-butyl ammonium hydroxide (TBAHmanufactured by Kanto Kagaku Co., Ltd.) were added to 28.57 g (2 g interms of solid content) of the oxidized cellulose prepared as mentionedabove, the oxidized cellulose having a solid content concentration of7%, to obtain 400 g of an oxidized cellulose suspension having a pH of10. The thus prepared suspension was treated with a mixer equipped witha rotary blade for 60 minutes, to obtain a fine cellulose fiberdispersion liquid.

Example 6 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 10% by weight of tetraethyl ammonium hydroxide wereadded to 114.29 g (8 g in terms of solid content) of the oxidizedcellulose prepared as mentioned above, the oxidized cellulose having asolid content concentration of 7%, to obtain 400 g of an oxidizedcellulose suspension having a pH of 10. The thus prepared suspension wastreated with a mixer equipped with a rotary blade for 60 minutes, toobtain a fine cellulose fiber dispersion liquid.

Example 7 Preparation of Fine Cellulose Fiber Dispersion Liquid

199 g of ethanol, distilled water, and 10% by weight of tetraethylammonium hydroxide were added to 28.57 g (2 g in terms of solid content)of the oxidized cellulose prepared as mentioned above, the oxidizedcellulose having a solid content concentration of 7%, to obtain 400 g ofan oxidized cellulose suspension having a pH of 10. The thus preparedsuspension was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid.

Comparative Example 3 Preparation of Fine Cellulose Fiber DispersionLiquid

Distilled water and an aqueous solution containing 0.5 N of sodiumhydroxide were added to 28.57 g (2 g in terms of solid content) of theoxidized cellulose prepared as mentioned above, the oxidized cellulosehaving a solid content concentration of 7%, to obtain 400 g of anoxidized cellulose suspension having a pH of 10. The thus preparedsuspension was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid.

Comparative Example 4 Preparation of Fine Cellulose Fiber DispersionLiquid

Distilled water and an aqueous solution containing 0.5 N of sodiumhydroxide were added to 114.29 g (8 g in terms of solid content) of theoxidized cellulose prepared as mentioned above, the oxidized cellulosehaving a solid content concentration of 7%, to obtain 400 g of anoxidized cellulose suspension having a pH of 10. The thus preparedsuspension was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid.

Comparative Example 5 Preparation of Fine Cellulose Fiber DispersionLiquid

199 g of ethanol, distilled water, and an aqueous solution containing0.5 N of sodium hydroxide were added to 28.57 g (2 g in terms of solidcontent) of the oxidized cellulose prepared as mentioned above, theoxidized cellulose having a solid content concentration of 7%, to obtain400 g of an oxidized cellulose suspension having a pH of 10. The thusprepared suspension was treated with a mixer equipped with a rotaryblade for 60 minutes, to obtain a fine cellulose fiber dispersionliquid.

(Measurement of Transmittance of the Fine Cellulose Fiber DispersionLiquid)

The fine cellulose fiber dispersion liquids prepared in Examples 3 to 7and Comparative Examples 3 to 5 were compared in terms of thetransparency thereof by measuring the transmittance thereof at 660 nmusing a spectrophotometer.

(Measurement of Viscosity of the Fine Cellulose Fiber Dispersion Liquid)

The shear viscosity of the fine cellulose fiber dispersion liquidsprepared in Examples 3 to 7 and Comparative Examples 3 to 5 was measuredby a rheometer (MARS manufactured by HAAKE Company) using a cone-plateunder conditions of an inclination angle of 1° and a cone diameter of 35mm. The shear viscosity was continuously measured for shear rates of0.01 to 100 s⁻¹ while maintaining the measurement site at 23° C., andthe value of the shear viscosity at the shear rate of 1 s⁻¹ wasdetermined. In addition, Ti values of the fine cellulose fiberdispersion liquids prepared in Examples 3 to 5 and Comparative Example 3were determined as ratios η1 s⁻¹/η10 s⁻¹ of the shear viscosity at theshear rate of 1 s⁻¹ relative to the shear viscosity at the shear rate of10 s⁻¹.

(Measurement of Contact Angle of the Fine Cellulose Fiber DispersionLiquid)

The contact angles of the fine cellulose fiber dispersion liquidsprepared in Examples 3 to 7 and Comparative Examples 3 to 5 relative tothe PET film base material (12 μm thickness, corona-treated surface)were measured using an automatic contact angle meter (CA-V typemanufactured by Kyowa Interface Science Co., Ltd.). The measurement wasperformed by a drop method, and the contact angles were measured 20seconds after drop-deposition.

(Cellulose Film)

The fine cellulose fiber dispersion liquids prepared in Examples 3 to 7and Comparative Examples 3 to 5 were poured into square plasticcontainers, and then dried at 50° C. overnight, followed by drying at120° C. for 1 hour to obtain cellulose films.

(Measurement of the Content of Sodium Ions)

The contents of sodium ions in the cellulose films were measured by anEPMA method using an X-RAY micro analyzer.

The transmittance of the fine cellulose fiber dispersion liquidsprepared in Examples 3 to 7 and Comparative Examples 3 to 5, the shearstress thereof, the Ti values thereof, the contact angle thereof, andthe sodium content of the cellulose films are shown in Table 2.

TABLE 2 Comparative Comparative Comparative Example 3 Example 4 Example5 Example 6 Example 7 Example 3 Example 4 Example 5 Alkali species TMAHTEAH TBAH TEAH TEAH NaOH NaOH NaOH Dispersion Water Water Water WaterWater/EtOH Water Water Water/EtOH medium Solid content 0.5 0.5 0.5 2 0.50.5 2 0.5 concentration (%) pH 10 10 10 10 10 10 10 10 Transmittance98.6 98.8 99.0 81.7 73.0 95.7 55.9 0.4 (%) Shear 1.277 0.855 0.08736.106 2.893 3.165 56.98 1.355 viscosity (s⁻¹) Ti value 5.35 4.46 3.395.82 4.32 8.02 8.12 2.6 Contact angle 62.4 60.4 59.7 65.2 34.1 61.3 85.220.5 (°) Na content Below Below Below Below Below 9.1 7.9 8.2 (wt %)measurable measurable measurable measurable measurable limits limitslimits limits limits

The transmittance of the fine cellulose fiber dispersion liquidsprepared in Examples 3 to 7 is larger than that of the fine cellulosefiber dispersion liquids prepared in Comparative Examples 3 to 5. On theother hand, the fine cellulose fiber dispersion liquids prepared inComparative Examples 4 and 5 were not sufficiently dispersed andmaintained to be clouded. The fine cellulose fiber dispersion liquidsprepared using the organic alkali exhibited a reduced viscosity andthixotropic properties. In the case where the alcohol was used in thedispersion medium, the contact angle relative to the base materialdecreased, and thereby improving the wettability. In the cellulose filmsprepared in Examples 3 to 7 in which the dispersion treatment wasperformed using the organic alkali, no sodium ions were detected.

Next, Examples 8 to 11 and Comparative Examples 6 to 9 will beexplained.

(Preparation of Oxidized Cellulose)

A bleached pulp of a needle-leaved tree commonly available was used as acellulose.

60 g of the cellulose (calculated in terms of the absolute dry massthereof) was added to 1000 g of distilled water and then stirred to beswollen, followed by fibrillating using a mixer. A solution composed of2200 g of distilled water, 0.6 g of TEMPO previously dissolved in 400 gof distilled water, and 6 g of sodium bromide was added to theresultant, and 172 g of an aqueous solution containing 2 mol/L of sodiumhypochlorite was added dropwise thereto to start oxidation reaction. Thereaction temperature was always maintained at 30° C. or lower. Althoughthe pH in the system during the reaction lowered, the pH was maintainedat 10 by gradually adding thereto an aqueous solution containing 0.5 Nof NaOH. The reaction was allowed to proceed for 4 hours whilemonitoring the addition amount of the NaOH aqueous solution, followed bymaking the reaction stop by adding 60 g of ethanol. Then, 0.5 N of HClwas added dropwise to the reaction liquid to lower the pH to 1.8. Thereaction liquid was filtered using a nylon mesh, followed by washing thesolid content thereof with water several times to remove the reactionreagents or by-products, and thereby obtaining an oxidized cellulosecontaining water, the solid content concentration of the resultant being7%.

(Measurement of the Introduction Amount of Functional Groups)

0.2 g of the moist oxidized cellulose, calculated in terms of theabsolute dry mass thereof, was put into a beaker, and distilled waterwas added thereto to amount to 60 g. 0.5 mL of an aqueous solutioncontaining 0.1 M of NaCl was added thereto, and the pH of the resultantwas adjusted to 1.8 using 0.5 M of hydrochloric acid, followed by addingan aqueous solution containing 0.5 M of NaOH dropwise to measure theconductivity of the resultant. The measurement was continued until thepH of the resultant reached approximately 11. An additive amount of NaOHat the neutralization stage of the weak acid, which corresponded to thecontent of carboxyl groups, was read from the obtained conductivitycurve to determine the content of carboxyl groups to be 2.0 mmol/g.

Next, 20 mL of 0.5 M acetic acid, 60 ml of distilled water, and 1.8 g ofsodium chlorite were added to 2 g of the moist oxidized cellulose,calculated in terms of the absolute dry mass thereof, and the pH of theresultant was adjusted to 4, followed by allowing the reaction toproceed for 48 hours. Then, the content of carboxyl groups was measuredas mentioned above, which revealed that the content thereof was 2.1mmol/g. As a result, the content of aldehyde groups was calculated to be0.1 mmol/g.

Example 8 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 10% by weight of tetraethyl ammonium hydroxide (TEAHmanufactured by Kanto Kagaku Co., Ltd) were added to 57.14 g (4 g interms of solid content) of the oxidized cellulose prepared as mentionedabove, the oxidized cellulose having a solid content concentration of7%, to obtain 400 g of an oxidized cellulose suspension having a pH of10. The thus prepared suspension was treated with a mixer equipped witha rotary blade for 60 minutes, to obtain a fine cellulose fiberdispersion liquid. 9.95 g of methanol and 0.05 g of distilled water wereadded to 10 g of the thus prepared fine cellulose fiber dispersionliquid, followed by stirring to obtain a fine cellulose fiber dispersionliquid having a solid content concentration of 0.5%.

Example 9

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Example 8, except that ethanol was used instead ofmethanol.

Example 10

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Example 8, except that 2-propanol (IPA) was usedinstead of methanol.

Example 11

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Example 8, except that acetone was used instead ofmethanol.

Comparative Example 6 Preparation of Fine Cellulose Fiber DispersionLiquid

Distilled water and an aqueous solution containing 0.5 N sodiumhydroxide (NaOH) were added to 57.14 g (4 g in terms of solid content)of the oxidized cellulose prepared as mentioned above, the oxidizedcellulose having a solid content concentration of 7%, to obtain 400 g ofan oxidized cellulose suspension having a pH of 10. The thus preparedsuspension was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid. 9.95 g ofmethanol and 0.05 g of distilled water were added to 10 g of the thusprepared fine cellulose fiber dispersion liquid, followed by stirring toobtain a fine cellulose fiber dispersion liquid having a solid contentconcentration of 0.5%.

Comparative Example 7

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Comparative Example 6, except that ethanol was usedinstead of methanol.

Comparative Example 8

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Comparative Example 6, except that 2-propanol (IPA)was used instead of methanol.

Comparative Example 9

A fine cellulose fiber dispersion liquid was prepared in a similarmanner to that of Comparative Example 6, except that acetone was usedinstead of methanol.

(Measurement of Transmittance of the Fine Cellulose Fiber DispersionLiquid)

The fine cellulose fiber dispersion liquids prepared in Examples 8 to 11and Comparative Examples 6 to 9 were compared in terms of thetransparency thereof by measuring the transmittance thereof at 660 nmusing a spectrophotometer. The measurement results are shown in Table 3.

TABLE 3 Comparative Comparative Comparative Comparative Example 8Example 9 Example 10 Example 11 Example 6 Example 7 Example 8 Example 9Alkali species TEAH TEAH TEAH TEAH NaOH NaOH NaOH NaOH Water-based WaterWater Water Water Water Water Water Water medium Water-soluble MethanolEthanol IPA Aceton Methanol Ethanol IPA Aceton organic solvent Solidcontent 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 concentration (%) pH 10 10 10 1010 10 10 10 Transmittance 98.6 99.3 99.2 98.2 96.0 81.7 81.6 77.0 (%)

In the fine cellulose fiber dispersion liquid prepared in Examples 8 to11, agglomeration and white turbidity were not visually observed and thetransmittance thereof was not decreased, without depending on thesolvent added. On the other hand, when ethanol, 2-propanol, or acetone,was added in the fine cellulose fiber dispersion liquid prepared inComparative Examples 6 to 9, agglomeration and white turbidity werevisually observed, which made the dispersion liquid heterogeneous, andthereby deteriorating the transmittance thereof. In other words, in thecase where sodium hydroxide was used as an alkali, the addition of thewater-soluble organic solvent to the prepared fine cellulose fiberdispersion liquid made the dispersed fine cellulose fibers agglomerate,and thereby generating agglomeration and white turbidity in the finecellulose fiber dispersion liquid, and making the fine cellulose fiberdispersion liquid heterogeneous.

Next, Examples 12 to 15 and Comparative Examples 10 and 11 will beexplained.

(Preparation of Oxidized Cellulose)

A bleached pulp of a needle-leaved tree commonly available was used as acellulose.

60 g of the cellulose (calculated in terms of the absolute dry massthereof) was added to 1000 g of distilled water and then stirred to beswollen, followed by fibrillating using a mixer. A solution composed of2200 g of distilled water, 0.6 g of TEMPO previously dissolved in 400 gof distilled water, and 6 g of sodium bromide was added to theresultant, and 172 g of an aqueous solution containing 2 mol/L of sodiumhypochlorite was added dropwise thereto to start oxidation reaction. Thereaction temperature was always maintained at 20° C. or lower. Althoughthe pH in the system during the reaction lowered, the pH was maintainedat 10 by gradually adding thereto an aqueous solution containing 0.5 Nof NaOH. The reaction was allowed to proceed while monitoring theadditive amount of the NaOH aqueous solution for 4 hours, followed bymaking the reaction stop by adding 60 g of ethanol. Then, 0.5 N of HCLwas added dropwise to the reaction liquid to lower the pH to 1.8. Thereaction liquid was filtered using a nylon mesh, followed by washing thesolid content thereof with water several times to remove the reactionreagents or by-products, and thereby obtaining an oxidized cellulosecontaining water, the solid content concentration of the resultant being7%.

(Measurement of the Introduction Amount of Functional Groups)

0.2 g of the moist oxidized cellulose, calculated in terms of theabsolute dry mass thereof, was put into a beaker, and distilled waterwas added thereto to amount to 60 g. 0.5 mL of an aqueous solutioncontaining 0.1 M of NaCl was added thereto, and the pH of the resultantwas adjusted to 1.8 using 0.5 M of hydrochloric acid, followed by addingan aqueous solution containing 0.5 M of NaOH dropwise to measure theconductivity of the resultant. The measurement was continued until thepH of the resultant reached approximately 11. An additive amount of NaOHat the neutralization stage of the weak acid, which corresponded to thecontent of carboxyl groups, was read from the obtained conductivitycurve to determine the content of carboxyl groups to be 2.0 mmol/g.

Next, 20 mL of 0.5 M acetic acid, 60 ml of distilled water, and 1.8 g ofsodium chlorite were added to 2 g of the moist oxidized cellulose,calculated in terms of the absolute dry mass thereof, and the pH of theresultant was adjusted to 4, followed by allowing the reaction toproceed for 48 hours. Then, the content of carboxyl groups was measuredas mentioned above, which revealed that the content thereof was 2.1mmol/g. As a result, the content of aldehyde groups was calculated to be0.1 mmol/g.

Example 12 Preparation of Fine Cellulose Fiber Dispersion Liquid

Distilled water and 10% by weight of tetraethyl ammonium hydroxide (TEAHmanufactured by Kanto Kagaku Co., Ltd) were added to 57.14 g (4 g interms of solid content) of the oxidized cellulose prepared as mentionedabove, the oxidized cellulose having a solid content concentration of7%, to obtain 400 g of an oxidized cellulose suspension having a pH of10. The thus prepared suspension was treated with a mixer equipped witha rotary blade for 60 minutes, to obtain a fine cellulose fiberdispersion liquid. 9.95 g of acetone and 0.05 g of distilled water wereadded to 10 g of the thus prepared fine cellulose fiber dispersionliquid, followed by stirring to obtain a fine cellulose fiber dispersionliquid having a solid content concentration of 0.5%.

Example 13

Distilled water and 10% by weight by weight of tetrabutylphosphoniumhydroxide (TBPH manufactured by Kanto Kagaku Co., Ltd.) were added to57.14 g (4 g in terms of solid content) of the oxidized celluloseprepared as mentioned above, the oxidized cellulose having a solidcontent concentration of 7%, to obtain 400 g of an oxidized cellulosesuspension having a pH of 10. The thus prepared suspension was treatedwith a mixer equipped with a rotary blade for 60 minutes, to obtain afine cellulose fiber dispersion liquid. 9.95 g of acetone and 0.05 g ofdistilled water were added to 10 g of the thus prepared fine cellulosefiber dispersion liquid, followed by stirring to obtain a fine cellulosefiber dispersion liquid having a solid content concentration of 0.5%.

Example 14

Distilled water and 0.1 N of ammonia aqueous solution were added to57.14 g (4 g in terms of solid content) of the oxidized celluloseprepared as mentioned above, the oxidized cellulose having a solidcontent concentration of 7%, to obtain 400 g of an oxidized cellulosesuspension having a pH of 10. The thus prepared suspension was treatedwith a mixer equipped with a rotary blade for 60 minutes, to obtain afine cellulose fiber dispersion liquid. 0.1 g of a water-solublepolycarbodiimide SV-02 (manufactured by Nisshinbo Industries, Inc.) wasadded to 10 g of the thus prepared fine cellulose fiber dispersionliquid. 9.95 g of acetone and 0.05 g of distilled water were added tothe resultant, followed by stirring to obtain a fine cellulose fiberdispersion liquid having a solid content concentration of 0.5%.

Example 15

Distilled water and 0.1 N of ammonia aqueous solution were added to57.14 g (4 g in terms of solid content) of the oxidized celluloseprepared as mentioned above, the oxidized cellulose having a solidcontent concentration of 7%, to obtain 400 g of an oxidized cellulosesuspension having a pH of 10. The thus prepared suspension was treatedwith a mixer equipped with a rotary blade for 60 minutes, to obtain afine cellulose fiber dispersion liquid. 0.05 g of EPOCROS WS-500(manufactured by Nippon Shokubai Co., Ltd.) was added to 10 g of thethus prepared fine cellulose fiber dispersion liquid. 9.95 g of acetoneand 0.05 g of distilled water were added to the resultant, followed bystirring to obtain a fine cellulose fiber dispersion liquid having asolid content concentration of 0.5%.

(Preparation of Laminate Body)

Polylactic acid (PLA) films, each having a film thickness of 25 μm, thesurface of which being subjected to plasma treatment, were used as basematerials. The fine cellulose fiber dispersion liquids prepared inExamples 12 to 15 were each coated on the plasma-treated surfaces of thebase materials using a bar coarter, followed by drying at 70° C. for 20minutes to obtain films (first coating film layers), each having a filmthickness of approximately 200 nm. On the first coating film layer as anundercoat layer, a gas-barrier material was coated with a bar coarter.As the gas-barrier material, a coating liquid containing a known finecellulose fiber was used. After the coating, the resultant was dried at70° C. for 30 minutes to form a gas barrier layer (second coating filmlayer) having a film thickness of approximately 0.5 μm.

In addition, a polypropylene (PP) film with a film thickness of 70 μmwas bonded on the gas barrier layer using an urethane polyol-basedadhesive agent by a dry laminate procedure to obtain a four-layeredlaminate body including the first coating film layer and the secondcoating film layer containing the gas-barrier material.

Comparative Example 10 Preparation of Fine Cellulose Fiber DispersionLiquid

Distilled water and an aqueous solution containing 0.5 N of sodiumhydroxide (NaOH) were added to 57.14 g (4 g in terms of solid content)of the oxidized cellulose prepared as mentioned above, the oxidizedcellulose having a solid content concentration of 7%, to obtain 400 g ofan oxidized cellulose suspension having a pH of 10. The thus preparedsuspension was treated with a mixer equipped with a rotary blade for 60minutes, to obtain a fine cellulose fiber dispersion liquid. 9.95 g ofacetone and 0.05 g of distilled water were added to 10 g of the thusprepared fine cellulose fiber dispersion liquid, followed by stirring toobtain a fine cellulose fiber dispersion liquid having a solid contentconcentration of 0.5%.

(Preparation of Laminate Body)

A four-layered laminate body containing a first coating film layerformed using the fine cellulose fiber dispersion liquid and a secondcoating film layer containing a gas-barrier material was prepared usingthe obtained fine cellulose fiber dispersion liquid in a similar mannerto that of Examples 12 to 15.

Comparative Example 11 Preparation of Laminate Body

A polylactic acid (PLA) film having a film thickness of 25 μm, thesurface of which was subjected to plasma treatment, was used as a basematerial. The same gas-barrier material as that used in Example 12 wascoated on the plasma-treated surface of the base material using a barcoarter, followed by drying at 70° C. for 30 minutes to form a gasbarrier layer having a film thickness of approximately 0.5 μm.

In addition, a polypropylene (PP) film with a film thickness of 70 μmwas bonded on the gas barrier layer using an urethane polyol-basedadhesive agent by a dry laminate procedure to obtain a three-layeredlaminate body including the gas-barrier layer.

(Measurement of Transmittance)

The fine cellulose fiber dispersion liquids prepared in Examples 12 to15 and Comparative Example 10 were compared in terms of the transparencythereof by measuring the transmittance thereof at 660 nm using aspectrophotometer. The measurement results are shown in Table 4.

<Evaluation of Wettability>

The laminate bodies prepared in Examples 12 to 15 and ComparativeExample were visually evaluated in terms of the wettability when thefine cellulose fiber dispersion liquid was coated on the PLA basematerial, and also the laminate bodies prepared in Examples 12 to 15 andComparative Examples 10 and 11 were visually evaluated in terms of thewettability when the gas-barrier material was coated on the undercoatlayer. The evaluation results are shown in Table 4.

<Evaluation of Adhesiveness>

With respect to the laminate bodies prepared in Examples 12 to 15 andComparative Example 10, the film formed using the fine cellulose fiberdispersion liquid on the base material was cut into a grid form composedof 10 vertical stripes and 10 horizontal stripes (with each interval of1 mm, total 100 cuts) using a cross cut guide “CCJ-1” (manufactured byCotec Co., Ltd.), followed by attaching thereon SELLOTAPE (trademark)(CT 24 manufactured by Nichiban Co., Ltd.) to perform a peeling test.After the peeling, the number of the cuts remaining on the base materialsurface without peeling therefrom (the number of remaining cuts/100) wascounted. The evaluation results are shown in Table 4.

<Measurement of Adhesion Strength>

Each laminate body prepared in Examples 12 to 15 and ComparativeExamples and 11 was cut in a rectangle having a width of 15 mm and alength of 10 cm to obtain a test specimen. The test specimen wassubjected to T-shaped peel test at a peeling rate of 300 mm/min tomeasure the adhesion strength (N/15 mm) between the base material andthe PP film in accordance with JIS-K-7127. The obtained measurementresults are shown in Table 4.

TABLE 4 Example Example Example Example Comparative Comparative 12 13 1415 Example 10 Example 11 Base material PLA PLA PLA PLA PLA PLA UndercoatAlkali species TEAH TBPH Ammonia Ammonia NaOH — layer Water-based mediumWater Water Water Water Water — (Fine Other additives Absence AbsenceSV-02 WS500 Absence — cellulose Organic solvent Acetone Acetone AcetoneAcetone Acetone — fiber Solid content concentration 0.5 0.5 0.5 0.5 0.5— dispersion (wt %) liquid) pH 10 10 10 10 10 — Evaluation Transmittance98 97 97 97 77 — (%) Wettability ∘ ∘ ∘ ∘ x — Adhesiveness 70/100 70/100100/100 100/100 0/100 — Functional Evaluation Wettability ∘ ∘ ∘ ∘ x xmaterial layer Adhesion 0.2 0.2 1.2 2.5 0 0 (gas-barrier strengthmaterial) (N)

As shown in Table 4, in Examples 12 to 15, the fine cellulose fiberdispersion liquid and the organic solvent were uniformly mixed to obtainthe fine cellulose fiber dispersion liquid having a high transparency.In addition, the undercoat layer (first coating film layer) formed onthe base material using the thus obtained fine cellulose fiberdispersion liquid had a high wettability with respect to the basematerial and had no eye hole. In addition, the adhesiveness of theundercoat layer to the base material was improved. In addition, thefunctional material layer (second coating film layer) containing thegas-barrier material had also a high wettability with respect to theundercoat layer and exhibited a high adhesion strength, and therebyimproving the coatability thereof.

On the other hand, in Comparative Examples 10 and 11, the wettabilitywith respect to the base material was low and no homogeneous coatingfilm was formed. Thus, it has been demonstrated that the fine cellulosefiber dispersion liquid according to the present invention is excellentin the transmittance, the wettability, the adhesiveness, and theadhesion strength, and allows to form various functional materialcoating film, such as a gas barrier layer or a water vapor barrierlayer, on the base material, with favorable coatability andadhesiveness. Accordingly, the use of the fine cellulose fiberdispersion liquid prepared by the manufacturing method of the finecellulose fiber dispersion liquid according to the present inventionmakes it possible to provide a mechanically stable laminate body havingan improved adhesiveness for the base material.

The present invention is not limited to the above-shown examples, andmay be variously modified without departing from the spirit of thepresent invention.

1. A method of manufacturing a fine cellulose fiber dispersion liquid,comprising: an oxidation process in which a cellulose is subjected to anoxidation treatment to obtain an oxidized cellulose; and a dispersionprocess in which the oxidized cellulose obtained in the oxidationprocess is subjected to a dispersion treatment in a water-based mediumin which a pH thereof is adjusted to 4 to 12 using either an ammoniawater or an organic alkali to obtain the fine cellulose fiber dispersionliquid.
 2. The method according to claim 1, wherein the organic alkaliis either an amine or an organic onium compound comprising a hydroxideion as a counter ion.
 3. The method according to claim 1, wherein theorganic alkali is a quaternary ammonium compound having a hydroxide ionas a counter ion.
 4. The method according to claim 1, wherein thewater-based medium is either water or a mixed liquid comprising waterand an alcohol, and the alcohol is methanol, ethanol, 1-propanol,2-propanol, 1-butanol, or 2-butanol.
 5. The method according to claim 1,wherein the water-based medium comprises a water-soluble organicsolvent, and the water-soluble organic solvent is at least one organicsolvent selected from the group consisting of methanol, ethanol,2-propanol, acetone, methyl ethyl ketone, 1,4-dioxane, tetrahydrofuran,N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide,acetonitrile, and ethyl acetate.
 6. The method according to claim 1,further comprising: a preparation process to be performed after thedispersion process by adding a water-soluble organic solvent to theobtained fine cellulose fiber dispersion liquid, the water-solubleorganic solvent being at least one organic solvent selected from thegroup consisting of methanol, ethanol, 2-propanol, acetone, methyl ethylketone, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide,N,N-dimethylacetamide, dimethylsulfoxide, acetonitrile, and ethylacetate.